The present disclosure relates to the field of image processing, and more specifically, the present disclosure relates to an image correction method for a direct marking system using input scaling.
Liquid ink printers of the type frequently referred to as continuous stream or as drop-on-demand, such as piezoelectric, acoustic, phase change wax-based, or thermal, have at least one printhead from which droplets of ink are directed towards a recording medium. Within the printhead, the ink is contained in a plurality of ink carrying conduits or channels. Power pulses cause the droplets of ink to be expelled as required from orifices or nozzles at the ends of the channels.
In a thermal ink-jet printer, the power pulse is usually produced by a heater transducer or a resistor, typically associated with one of the channels. Each resistor is individually addressable to heat and vaporize ink in the channels. As voltage is applied across a selected resistor, a vapor bubble grows in the associated channel and initially bulges toward the channel orifice followed by collapse of the bubble. The ink within the channel then retracts and separates from the bulging ink thereby forming a droplet moving in a direction away from the channel orifice and towards the recording medium whereupon hitting the recording medium a dot or spot of ink is deposited. The channel is then refilled by capillary action, which, in turn, draws ink from a supply container of liquid ink.
The ink-jet printhead may be incorporated into either a carriage type printer, a partial width array type printer, or a page-width type printer. The carriage type printer typically has a relatively small printhead containing the ink channels and nozzles. The printhead can be sealingly attached to a disposable ink supply cartridge and the combined printhead and cartridge assembly is attached to a carriage which is reciprocated to print one swath of information (equal to the length of a column of nozzles), at a time, on a stationary recording medium, such as paper or a transparency. After the swath is printed, the paper is stepped a distance equal to the height of the printed swath or a portion thereof, so that the next printed swath is contiguous or overlapping therewith. This procedure is repeated until the entire page is printed.
In contrast, the page width printer includes a stationary printhead having a length sufficient to print across the width or length of a sheet of recording medium at a time. The recording medium is continually moved past the page width printhead in a direction substantially normal to the printhead length and at a constant or varying speed during the printing process. A page width ink-jet printer is described, for instance, in U.S. Pat. No. 5,192,959.
Printers typically print color and/or monochrome images received from an image output device or document creator such as a personal computer, a scanner, or a workstation. The color images printed are produced by printing with several colored inks or colorants of different colors at a time. The color of the ink and amount of ink deposited by the printer is determined according to image information received from the document creator. The document creator provides an input digital gray-scale image, which is either defined in monochromatic terms, colorimetric terms, or both. The amount of gray level is typically defined by an input pixel value ranging from 0 to 255, where 0 is equal to white, 255 is equal to black, and value therebetween are shades of gray. Commonly this description may be part of a Page Description Language (PDL) file describing the document. In the case of computer generated images, colors defined by the user at the user interface of a workstation can be defined initially in color space of tristimulus values. These colors are defined independently of any particular device, and accordingly reference is made to the information as being “device independent”.
The printer, on the other hand, has an output which is dependent on the device or “device dependent”. This dependency is due, in part, to the fact that while the input digital gray scale image includes pixels having a wide range of gray scale values, the output image generated by the printer is a binary image formed from a plurality of ink drops or spots wherein the absence of a spot defines the level of white and the presence of a spot defines black. Consequently, a transformation must be made from the input digital gray scale image to the printed binary image since the binary image includes binary information which either has a gray level value of zero (white) or one (black), but not levels of gray therebetween. These transformations, from an input image to an output image, are made with a number of known algorithms, including an algorithm known as the error diffusion algorithm which converts the input gray scale image into high frequency binary texture patterns that contain the same average grayscale information as the input image.
Color printers also include an output which can be defined as existing in a color space called CMYK (cyan-magenta-yellow-key or black) which is uniquely defined for the printer by its capabilities and colorants. Such printers operate by the addition of overlapping multiple layers of ink or colorant in layers to a page. The response of the printer tends to be relatively non-linear. These colors are defined for a particular device, and accordingly reference is made to the information as being device dependent. Thus, while a printer receives information in a device independent color space, it must convert that information to print in a device dependent color space, which reflects a possible range of colors of the printer; and secondly, printing of that image with a color printer in accordance with the colors defined by the scanner or computer generated image.
Various printers and methods for printing images on a recording medium are illustrated and described in the following disclosures which may be relevant to certain aspects of the present disclosure.
In U.S. Pat. No. 4,680,645 to Dispoto et al., a method for rendering gray scale images with variable dot sizes is described. An error diffusion algorithm is used in conjunction with a printing technique that is capable of producing a range of dot sizes on paper. The error diffusion algorithm is used to determine the error of a dot whenever the dot is printed. The error is then diffused to adjacent pixels where instead of being used for weighting the pixel in a thresholding process, the error is used to determine the proper dot size for the pixel.
U.S. Pat. No. 5,045,952 to Eschbach describes a method of dynamically adjusting the threshold level of an error diffusion algorithm to selectively control the amount of edge enhancement introduced into an encoded output. The threshold level is selectively modified on a pixel by pixel basis.
U.S. Pat. No. 5,343,231 to Suzuki describes an image recording apparatus capable of correcting density unevenness. A test pattern is recorded and the degree of density unevenness of the recording elements of the recording head are calculated by reading the test pattern. The temperature of the recording head is detected and the degree of calculated density unevenness is corrected according to the detected temperature.
U.S. Pat. No. 5,375,002 to Kim et al. describes an error diffusion circuit and a method for adaptively compensating for the distortion of brightness and color with respect to neighboring pixels. An error diffusion circuit includes a color determining portion for adding CMY signals to a diffusion error to generate a current pixel value, comparing the current pixel value with sequentially supplied error lookup data to determine an address of error lookup data having the smallest error as output pixel color information, and applying the output pixel color information to the printer.
U.S. Pat. No. 5,434,672 to McGuire describes a pixel error diffusion method. Error distribution in printing and information processing systems is accomplished according to combined internal and external superpixel error diffusion techniques. For a particular superpixel, error amounts of a selected internal subject pixel are provided to another internal subject pixel until a determined or selected final pixel error value within the selected superpixel has been determined. The final internal error value is distributed among selected superpixels within a predetermined superpixel neighborhood.
“Threshold Modulation In Error Diffusion” by Knox and Eschbach, Journal of Electronic Imaging, July 1993, vol. 2, Pages 185 to 192, describes a theoretical analysis of threshold modulation in error diffusion. Spatial modulation of the threshold is shown to be mathematically identical to processing an equivalent input image with a standard error diffusion algorithm.
U.S. Pat. No. 5,847,724 to Mantell describes a method of printing an input digital gray-scale image by ejecting ink on recording medium through a plurality of ink ejecting orifices to form a binary image including a plurality of spots. The method of printing includes the steps of determining an ink spot characteristic or ink ejecting characteristic for at least one of the plurality of ink ejecting orifices, calculating a correction factor based on the characteristic, modifying an error diffusion algorithm with the calculated correction factor, and printing the binary image according to the modified error diffusion algorithm on the recording medium.
U.S. Pat. No. 6,068,361 to Mantell describes a method for rendering grayscale images with variable number of drops. An error diffusion algorithm is used in conjunction with a printing technique that is capable of producing multiple drops per pixel. The error diffusion algorithm is used to determine the error of a number of dots whenever a given number of dots are printed. The error is then diffused to adjacent pixels.
With respect to a direct marking system, where an ink-jet printer is used to print directly on a product or part, such as a microchip, plastic and metal components, and glass, the error correction methodologies described above are not always feasible or may require more calculations than needed for the direct marking system.